A skeletal muscle generates action potentials when contracting and expanding by nerve stimulation from the brain. An evaluation system, which detects the action potentials and evaluates muscle abnormalities and levels of fatigue based on an electromyogram (electromyogram: EMG) being a waveform of the action potentials, can be developed. However, when the action potentials are detected while the skeletal muscle contracts and expands, an electrical signal resulting from stimulation from the brain and an action potential generated by the muscle during exercise are included as noise; accordingly, the state of activity of the muscle is not able to be stably evaluated.
Hence, an evaluation system has been proposed which adds an electrical stimulation signal to a skeletal muscle, detects a muscle action potential evoked by the nerve stimulation of the electrical stimulation signal from a detection electrode in intimate contact with a body surface of the skeletal muscle, and evaluates the state of activity of the muscle. When a peripheral nerve of a muscle to be evaluated is innervated by an electrical stimulation signal, excitation reaches the muscle via a motor nerve to generate, in the muscle, muscle action potentials that cause the muscle to contract. The waveform of the muscle action potentials is called the M-wave. The muscle action potentials are detected from the body surface of the muscle; accordingly, an evoked electromyogram of the M-wave can be obtained. On the other hand, when the peripheral nerve is innervated, excitation also reaches the spine via a sensory nerve. α-cells are excited via a monosynaptic reflex. Muscle action potentials that cause the muscle to contract are then generated via a motor nerve. The waveform of the muscle action potentials generated later than the M-wave is called the H-wave. In related muscle evaluation systems, the state of activity of the muscle is evaluated based on the amplitude of the M-wave or H-wave.
Of them, an evoked electromyography apparatus 3 disclosed in JP-A-2005-144108 includes a stimulation terminal fixing purpose belt 1 that brings a stimulating electrode 1-1 into intimate contact with a body surface of a site, in which the tibial nerve travels, of the popliteal fossa, a recording terminal fixing purpose belt 2 that brings a plurality of myoelectric detection electrodes 2-1, 2-1 . . . respectively into intimate contact at different positions with a body surface along the soleus of which state of activity is evaluated, a stimulation generation device 3-1 that outputs an electrical stimulation signal to the stimulating electrode 1-1, a recording device 3-2 that records muscle action potentials detected by the myoelectric detection electrodes 2-1, 2-1 . . . , and a processing device 3-3 that evaluates the state of activity of the soleus from an evoked electromyogram, as illustrated in FIG. 15.
In the evoked electromyography apparatus 100, an electrical stimulation signal is output to the stimulating electrode 101 to detect the amplitude of the H-wave from the myoelectric detection electrodes 103, 103 . . . . The amplitude of the H-wave represents the amount of activity of the muscle being the amount of stimulation from the spinal motor neurons for the soleus. Accordingly, the amplitudes of the H-wave detected at rest and during exercise are compared to evaluate the state of activity of the soleus.
Moreover, an apparatus for evaluating the level of activity of a muscle, the apparatus being disclosed in JP-A-2001-276005, measures an evoked electromyogram of the M-wave from myoelectric detection electrodes in intimate contact with a body surface along the direction of the muscle fibers in addition to a body surface of a muscle where an electrical stimulation signal is measured, and evaluates the activity level and fatigue level of the muscle from the amplitude of the M-wave.
Furthermore, a method for assisting in determining the presence or absence of a disorder of excitation-contraction coupling, the method being disclosed in JP-A-2015-66401, adds an electrical stimulation signal to evaluate a disorder of muscle in combination with an evoked electromyogram EMG detected from a body surface and an evoked mechanomyogram (mechanomyogram: MMG) evoked by the electrical stimulation signal. The evoked mechanomyogram MMG is a vibration waveform obtained by recording a mechanical variable in a major axis direction of the muscle involved with contraction induced by electrical stimulation. The evoked mechanomyogram MMG is considered as a kind of pressure wave that vibrates in a frequency band equal to or less than 100 Hz that is smaller by one order of magnitude than the frequency band of the evoked electromyogram EMG. In JP-A-2015-66401, a myoelectric detection electrode and an accelerometer are fixed onto a body surface of a muscle to be measured, and onto a body surface of the belly of the muscle where the amplitude of the muscle is at its maximum, respectively, with adhesive tape. A single electrical stimulation signal of 1 Hz is added to a body surface near the muscle to detect the evoked electromyogram EMG from the myoelectric detection electrode and detect the evoked mechanomyogram MMG from the accelerometer.
The difference in distal latency between the detected evoked electromyogram EMG and evoked mechanomyogram MMG is obtained. If the difference in distal latency is increased as compared to one under normal conditions, or if the amplitude of the evoked mechanomyogram MMG dwindles although the amplitude of the evoked electromyogram EMG is constant, it is evaluated as having a disorder of excitation-contraction coupling. According to the invention of JP-A-2015-66401, the evoked electromyogram EMG and the evoked mechanomyogram MMG are used in combination; accordingly, it is possible to determine a disorder of excitation-contraction coupling correctly and excellently in reproducibility.
As described above, the state of activity of a muscle can be evaluated based on the amplitude of the evoked electromyogram EMG and the difference in distal latency between the evoked electromyogram EMG and the evoked mechanomyogram MMG. However, the amplitude of the evoked electromyogram EMG and the distal latencies of the evoked electromyogram EMG and the evoked mechanomyogram MMG vary according to the stimulation position to which an electrical stimulation signal is applied and the distance between the stimulation position and the myoelectric detection electrode or the accelerometer that detects evoked muscle sound.
However, in any evaluation system described in JP-A-2005-144108, JP-A-2001-276005, and JP-A-2015-66401, the stimulation position to which an electrical stimulation signal for a muscle to be evaluated is applied is not clear, and the myoelectric detection electrode and the accelerometer that detects evoked muscle sound are not brought into intimate contact with the body surface, at the positions predetermined distances away from the stimulation position. Accordingly, it is not possible to quantitatively detect the amplitude and distal latency of the evoked electromyogram EMG or the evoked mechanomyogram MMG and correctly evaluate the state of activity of the muscle.
Especially in the evaluation system of JP-A-2015-66401, an electrical stimulation signal cannot be applied to a fixed position during exercise. Accordingly, it is not possible to evaluate a load and the state of activity of the muscle while a load is applied to the muscle; therefore, it is not possible to observe secular changes in the state of activity of the muscle in real time during exercise.
Moreover, the inventor of the present application has found that when muscle fatigue increases due to exercise, the propagation speed of the M-wave caused by an electrical stimulation signal reduces, and there is a correlation between muscle fatigue and the propagation speed. However, the propagation speed of the M-wave is obtained based on the time (latency) between when the electrical stimulation signal is applied to when the myoelectric detection electrode detects the M-wave, and the interval between the stimulation position and the myoelectric detection electrode or between the myoelectric detection electrodes. Accordingly, in the related evaluation systems where these intervals are unknown cannot evaluate the level of fatigue of a muscle caused by exercise based on the propagation speed of the M-wave.
Furthermore, a muscle to be measured is under the body surface. Accordingly, the myoelectric detection electrode cannot be brought into intimate contact with the body surface at a position along the muscle fibers; hence, a correct evoked electromyogram cannot be obtained.
The present disclosure has been made considering such problems, and an object thereof is to provide a muscle condition measurement sheet that can quantitatively detect the amplitude and latency of an evoked electromyogram EMG or an evoked mechanomyogram MMG and correctly evaluate the state of activity of a muscle.
Moreover, another object is to provide a muscle condition measurement sheet that can evaluate the state of activity of a muscle in real time even during an exercise where a load is applied to the muscle.
Another object is to provide a muscle condition measurement sheet that evaluates the level of fatigue of a muscle based on a latency of a myoelectric detection electrode in detection.